Construction materials with engineered sound attenuating properties and methods therefor

ABSTRACT

A sound attenuation material includes a plurality of particles, each having a core and an elastic or compliant coating around the core, and a matrix surrounding the plurality of particles, the matrix being less dense than the core. A method of manufacturing sound attenuating materials includes adding an elastic or compliant coating to core particles and drying and/or curing the coating, mixing the coated core particles into a matrix material, and pouring the mixture into a mold. The core particles are denser than the matrix material.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. application Ser. No.15/785,363, filed Oct. 16, 2017, which claims the benefit of U.S.Provisional Application No. 62/408,666, filed Oct. 14, 2016, each ofwhich is hereby incorporated by reference in its respective entirety.

FIELD OF THE DISCLOSURE

The application relates to the field of construction materials, and moreparticularly to sound attenuating construction materials.

BACKGROUND

Existing sound attenuation materials are expensive to manufacture andinstall, have high mass and/or weight, and/or fail to provide adequatesound attenuation.

As such, needs exist for improved sound attenuation materials.

SUMMARY

It is to be understood that both the following summary and the detaileddescription are exemplary and explanatory and are intended to providefurther explanation of the invention as claimed. Neither the summary northe description that follows is intended to define or limit the scope ofthe invention to the particular features mentioned in the summary or inthe description.

In certain embodiments, the disclosed embodiments may include one ormore of the features described herein.

A new sound attenuation material includes a plurality of particles, eachcomprising a core and an elastic or compliant coating around the core,and a matrix surrounding the plurality of particles, where the core isdenser than the matrix. The core may also be denser than the elastic orcompliant coating. The elastic or compliant coating may include fillermaterial having a density lower than that of the matrix, such as polymeror glass micro-balloons. The particles may be spherical or anothershape, such as irregular shards, and may be of various shapes. Theplurality of particles may include several different masses ofparticles. The matrix may be a construction material. The matrix mayinclude gypsum, cement, concrete, polymer, or ceramic. The matrix may befoamed. The matrix may include reinforcing fillers, which may includeone or more of polypropylene fibers, gravel, sand, carbon nanotubes,starch additives, paper fibers, and glass fibers.

The core of at least one of the plurality of particles may be metal,mineral, or ceramic (e.g., steel or tungsten). The elastic coating of atleast one of the plurality of particles may be an elastomeric polymer.The elastic coating of at least one of the plurality of particles may bepolyurethane, silicone, or rubber.

The core of at least one of the plurality of particles may have adiameter of 10 nm to 100 cm and density of 2.0 to 20 g/cc, and theelastic coating of the at least one of the plurality of particles mayhave a thickness of 10 nm to 20 mm, an elastic modulus of 0.005-0.5 GPa,and a density of 0.01 to 2.0 g/cc. In some embodiments, the core of theat least one of the plurality of particles has a diameter of 1 mm to 5cm, and the elastic coating of the at least one of the plurality ofparticles has a thickness of 0.1 mm to 10 mm, an elastic modulus of 0.01to 0.1 GPa, and a density of 0.05 to 0.3 g/cc.

A new method of manufacturing sound attenuating materials includesadding an elastic or compliant coating to core particles and dryingand/or curing the coating, mixing the coated core particles into amatrix material, and pouring the mixture into a mold. The core particlesare denser than the matrix material and may also be denser than theelastic or compliant coating. The method may also include drying themixture. The core particles may have a range of masses. Each mass ofcore particle corresponds to a resonant frequency, and the masses of thecore particles are selected based on pre-selected frequencies to beattenuated by a final construction material. The proportion of each masscore particle is selected based on a predetermined desired level ofattenuation at the corresponding resonant frequency. The method may alsoinclude foaming the matrix material by air- or gas-entrainment, blowingagents, polyurethane reactions, or vacuum application.

These and further and other objects and features of the invention areapparent in the disclosure, which includes the above and ongoing writtenspecification, with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated herein and form a partof the specification, illustrate exemplary embodiments and, togetherwith the description, further serve to enable a person skilled in thepertinent art to make and use these embodiments and others that will beapparent to those skilled in the art.

FIG. 1 illustrates a composite material with designer filler materialfor sound attenuation, according to an embodiment of the presentinvention.

FIG. 2A illustrates a composite sound-attenuating panel, according to anembodiment of the present invention.

FIG. 2B illustrates sound attenuation in the composite panel of FIG. 2A,according to an embodiment of the present invention.

FIG. 3 is a size distribution comparison of uncoated and coated tungstenparticles.

FIG. 4 illustrates an acoustic attenuation test conducted on a panelsimilar to or the same as that shown in FIG. 2A.

FIG. 5 shows impedance tube testing results for a wallboard according toan embodiment of the present invention, as well as controls.

FIG. 6 shows STC values from impedance tube, thickness, and density forthe same samples as FIG. 5 .

FIG. 7 shows ultrasonic testing results for commercial wallboardsamples.

FIG. 8 shows ultrasonic testing results for a wallboard sample accordingto an embodiment of the present invention, as well as a control.

FIG. 9 shows impact sound testing for two cement samples according toembodiments of the present invention, as well as a control.

FIG. 10 shows impact sound testing for a concrete sample according to anembodiment of the present invention, as well as a control.

FIG. 11 shows sound transmission results from a tapping machine for aconcrete sample according to an embodiment of the present invention, aswell as a control.

FIG. 12 shows a method of manufacturing sound attenuating materials,according to an embodiment of the present invention.

FIG. 13 is a schematic diagram showing a sound attenuating particlecontaining multiple cores, according to an embodiment of the presentinvention.

DETAILED DESCRIPTION

This application details construction materials with engineered soundattenuating properties, and methods therefor, in terms of variousexemplary embodiments. This specification discloses one or moreembodiments that incorporate features of the invention. Theembodiment(s) described, and references in the specification to “oneembodiment”, “an embodiment”, “an example embodiment”, etc., indicatethat the embodiment(s) described may include a particular feature,structure, or characteristic. Such phrases are not necessarily referringto the same embodiment. When a particular feature, structure, orcharacteristic is described in connection with an embodiment, personsskilled in the art may effect such feature, structure, or characteristicin connection with other embodiments whether or not explicitlydescribed.

In the several figures, like reference numerals may be used for likeelements having like functions even in different drawings. Theembodiments described, and their detailed construction and elements, aremerely provided to assist in a comprehensive understanding of theinvention. Thus, it is apparent that the present invention can becarried out in a variety of ways, and does not require any of thespecific features described herein. Also, well-known functions orconstructions are not described in detail since they would obscure theinvention with unnecessary detail. Any signal arrows in thedrawings/figures should be considered only as exemplary, and notlimiting, unless otherwise specifically noted.

The description is not to be taken in a limiting sense, but is mademerely for the purpose of illustrating the general principles of theinvention, since the scope of the invention is best defined by theappended claims.

It will be understood that, although the terms first, second, etc. maybe used herein to describe various elements, these elements should notbe limited by these terms. These terms are only used to distinguish oneelement from another. For example, a first element could be termed asecond element, and, similarly, a second element could be termed a firstelement, without departing from the scope of example embodiments. Asused herein, the term “and/or” includes any and all combinations of oneor more of the associated listed items. As used herein, the singularforms “a”, “an” and “the” are intended to include the plural forms aswell, unless the context clearly indicates otherwise.

It should also be noted that in some alternative implementations, thefunctions/acts noted may occur out of the order noted in the figures.For example, two figures shown in succession may in fact be executedsubstantially concurrently or may sometimes be executed in the reverseorder, depending upon the functionality/acts involved.

In embodiments of the present invention, sound absorbing panels,coatings, and foams are created through incorporation of designer fillermaterials. The fillers are layered particulates with specific geometriesand mechanical properties that impart particular sound attenuatingproperties.

FIG. 1 illustrates a composite material with designer filler materialfor sound attenuation, according to an embodiment of the presentinvention. As shown in FIG. 1 , the particles consist of a dense core110 (which may or may not be foamed) surrounded by an elastic orcompliant coating 120 (which may or may not be foamed). They arecharacterized by their layered structure and mechanical properties. Theparticles act as locally resonant structures within a surrounding matrix130.

FIG. 2A illustrates a composite sound-attenuating panel, according to anembodiment of the present invention. FIG. 2A shows particles such asthose illustrated in FIG. 1 , where the surrounding matrix 130 isconfigured into a plaster board, which may be used as a buildingmaterial. The dense core 110 can oscillate within the elastic coating120, which is positioned in the matrix 130, attenuating sound energydepending on its frequency as shown in FIG. 2B.

FIG. 2B illustrates sound attenuation in the composite panel of FIG. 2A,according to an embodiment of the present invention. At and around theresonant frequency of the dense cores, the cores vibrate, absorbing thesound energy and transforming it into kinetic energy, reducing the soundenergy which is delivered to the other side of the matrix (e.g., plasterboard). In FIG. 2B, the sound source 200 is emitting a sound 202, whichis partially reflected 204 by the board 206 and partially transmitted208 through the board. However, the transmitted sound energy 208 isattenuated by absorption of the sound energy by particles 210 as thesound energy passes through them, causing them to vibrate as shown bythe bands around the particles 210.

The matrix may be gypsum, cement, concrete, polymer, ceramic, or anothermaterial in which the particle filler can be embedded. Foamed versionsof these materials may also incorporate the filler. Foaming may beachieved through known methods such as air- or gas-entrainment, blowingagents, polyurethane reactions, or vacuum application. The matrixmaterial may also include additional structural components such asreinforcing fillers, and may be incorporated in a composite structureitself, such as a laminated panel. These materials have excellent soundabsorbing properties at low weight. Reinforcing fillers may be thoseknown to be of use in the matrix material in various circumstances, suchas polypropylene fibers, gravel, sand, carbon nanotubes, etc. Forexample, commercial gypsum wallboard often includes starch additives,paper fibers, glass fibers, etc. Gypsum wallboard in which particlefiller is included for sound attenuation purposes may also retain theseother fillers.

The dense core may be metal, mineral, or ceramic. The core is preferablysteel or tungsten but may be any material that is denser than thesurrounding matrix. The elastic coating may be polyurethane, silicone,rubber, or any other elastomeric polymer. The elastic coating is itselfpreferably filled with low density filler, such as polymer or glassmicro-balloons, in order to control its mechanical properties and,importantly, its density and the total density of the particles. By wayof example, low-density filler in the elastic matrix may make theparticles softer, which may be advantageous in some applications.

The particles may have a core size of 10 nm to 100 cm, in someembodiments 1 mm to 5 cm, core density of 2.0 to 20 g/cc, coatingthickness of 10 nm to 20 mm, in some embodiments 0.1 mm to 10 mm,coating elastic modulus of 0.005-0.5 GPa, in some embodiments 0.01 to0.1 GPa, and coating density of 0.01 to 2.0 g/cc, in some embodiments0.05 to 0.3 g/cc. Larger particles may be used in large compositestructures, such as concrete slabs and walls used for highway soundisolation, to achieve very low frequency sound attenuation. In concreteslabs, large particles of about 5 cm or up to 20 cm may be used.

The acoustic band gap frequency of the composite material depends on thesize and density of the core as well as the elastic modulus of theelastic coating of the filler particles. The attenuation frequency rangegenerally increases with decreasing particle core size and broadens withparticle core size distribution. Each particle size has a differentfrequency response, and the amount of attenuation achieved at a givenfrequency is primarily a factor of the concentration of the particleswith the appropriate frequency response. Therefore, fewer particles at agiven size and more particles at nearby sizes will reduce theattenuation at the frequency corresponding to the given size, butincrease attenuation at the frequencies correlating to the nearby sizes,effectively reducing magnitude of attenuation while broadening theattenuation effect across the frequency spectrum. In this way, the soundattenuating properties of the composite can be controlled. Multipleparticle sizes can be combined to cover larger frequency spans,resulting in broadband sound isolation in the audible range, similar toexamples 8 and 11 detailed below. Alternatively, select frequencies canbe isolated for designer sound attenuating properties. By selecting lowfrequencies for attenuation, vibration isolation may be achieved, forexample in roadways and other structures such as bridge or buildingfoundations. Vibration isolation may improve material durability. Totalfiller particle concentrations must be kept at levels that ensureadequate mechanical strength of the overall material for the givenapplication. In some instances, excessively high filler particleconcentrations result in unacceptable material weakness. The describedsound-attenuating materials may also exhibit superior crack propagationperformance, as cracks in the matrix material may be halted at theintersection of the matrix material with a filler particle.

The particles may be created by a variety of coating methods that resultin a layered structure with an inner core and outer coating. The coatingis preferably well distributed over the particles. In some embodiments,there may be multiple cores per particle. Such multiple-core particlesmay result from manufacturing a block of cores in matrix material andthen shredding the block to obtain the individual particles. Preferredcoating methods include pan-coating and/or fluidized bed coating.Particles are rolled in a drum and/or fluidized in a bed and the coatingmaterial precursor solution is applied, often while being dried and/orcured with hot air and/or moisture. Other types of mixers may also beused to produce the particles. Coating thickness and uniformity areimportant for very precise control of particle density; however,acceptable sound attenuation may often be achieved without such precisedensity or shape control. Therefore, the use of manufacturing methodsthat produce highly spherical particles may depend on the cost versusthe density control needed for a given application.

By controlling the coating thickness, and using a coating and coredensity that span that of the matrix precursor, the density of theparticles can be tuned to match the surrounding matrix. This isimportant to achieve ideal particle distribution throughout the matrixand to prevent separation due to differences in the matrix precursordensity and the particle density. An even distribution of the coating onthe particles leads to uniform density to avoid settling or floating ofparticles with different densities. In the case of multiple particlesizes in the same material, the densities of each can be matched to thematrix to ensure homogeneous dispersion in the surrounding matrix.

Example 1: Preparation of Coated ¼″ Diameter Steel Cores

Particles consisting of ¼″ diameter steel ball cores encapsulated in anelastic coating were prepared in a lab scale pan coater. A polymersolution was prepared by dispersing 226 g polydimethylsiloxane (100%Silicone Sealant from DAP) and 6.8 g acrylic microspheres (920 DE80 d30from Akzo Nobel) in 912 g mineral spirits (Odorless Mineral Spirits fromKlean Strip). The pan coater was charged with 500 g of steel cores (LowCarbon Steel Balls from McMaster Carr). The density of the startingsubstrate was 7.7 g/cm³. Hot air at 80° C. was blown onto the particlebed during the coating process. The polymer mixture (25° C.) was sprayedonto the steel cores at a rate of 7 mL/min with an air atomized spraygun (WA740 HVLP Plus from Walther Pilot). The coating process wascarried out over a period of 8 hrs. The discharged particles exhibitedhigh uniformity and maintained the same degree of sphericity androundness as the starting core material (>0.9 Krumbein-Sloss shapefactors). The resulting particles had a diameter of 10.8+/−0.2 mm,coating thickness of 2.2 mm, and density of 1.9 g/cm³.

Example 2: Preparation of Coated ⅛″ Diameter Steel Cores

Particles consisting of ⅛″ diameter steel ball cores encapsulated in anelastic coating were prepared in accordance with the aforementionedprocedure. Through the layered coating approach, the density of theparticles was reduced from 7.7 g/cm³ (uncoated) to 2.0 g/cm³ (coated).The resulting particles had a diameter of 5.4+/−0.3 mm and a coatingthickness of 1.1 mm.

Example 3: Preparation of Coated 1/16″ Diameter Steel Cores

Particles consisting of 1/16″ diameter steel ball cores encapsulated inan elastic coating were prepared in accordance with the aforementionedprocedure. Through the layered coating approach, the density of theparticles was reduced from 7.7 g/cm³ (uncoated) to 2.2 g/cm³ (coated).The resulting particles had a diameter of 2.6+/−0.3 mm and a coatingthickness of 0.5 mm.

Example 4: Preparation of Coated 0.8 mm Diameter Tungsten Cores

Particles consisting of 0.8+/−0.1 mm diameter tungsten carbide pelletsencapsulated in an elastic coating were prepared in a pan coater. Apolymer solution was prepared by dispersing 383 g polydimethylsiloxane(100% Silicone Sealant from DAP) and 11.5 g acrylic microspheres (920DE80 d30 from Akzo Nobel) in 1160 g mineral spirits (Odorless MineralSpirits from Klean Strip). The pan coater was charged with 500 g oftungsten pellets (20/40 Tungsten Carbide pellets from TungCo). 20/40pellets have 90% of their particles between 20 and 40 mesh (U.S.Standard Sieve Series) as described in ASTM E-11. Hot air at 80° C. wasblown onto the particle bed during the coating process. The polymermixture (25° C.) was sprayed onto the tungsten cores at a rate of 14mL/min with an air atomized spray gun. The coating process was carriedout over a period of 8 hrs. The discharged particles were uniform insize and exhibited an equivalent degree of sphericity and roundness asthe starting core material (>0.9 Krumbein-Sloss shape factors). Theresulting particles had a diameter of 1.7+/−0.4 mm, coating thickness of0.45 mm, and density of 2.1 g/cm³.

The size distribution (fraction 310 at each diameter 320) of theuncoated tungsten and coated particles are graphically illustrated inFIG. 3 . The uncoated tungsten is smaller in size and has a tighterdistribution, with a peak fraction of between 0.4 and 0.45 at a diameterof 0.9 mm and all falling between 0.6 mm and 1.1 mm, compared to a peakfraction of the coated particles of just over 0.15 at 1.7 mm diameterand a size range of 1 mm to 2.2 mm.

The results of the tests from Examples 1˜4 are also set forth in Table1.

TABLE 1 Particle characterization results comparing different substratesizes and materials Coated Std. Core Std. Dev. Core Particle Dev. OfParticle Coating Diameter Of Mean Density Diameter Mean DensityThickness Core Material mm mm g/cc mm mm g/cc mm Steel Balls 6.4 +/−0.17.7 10.8 +/−0.2 1.9 2.2 Steel Balls 3.2 +/−0.1 7.7 5.4 +/−0.3 2 1.1Steel Balls 1.6 +/−0.1 7.7 2.6 +/−0.3 2.2 0.5 Tungsten Carbide 0.8+/−0.1 15.6 1.7 +/−0.4 2.1 0.45 Pellets

Example 5: Preparation of Plaster Board with Particles from Example 1

To 1 part water was added, by sifting, 2 parts plaster, which wereallowed to soak for 1 min. The slurry was mixed in a Fann blender for 60sec at 4000 rpm. Separately, 0.1 g of foaming agent (“MasterCell 30”from BASF) and 4 g of water were mixed at 4000 rpm for 60 sec togenerate a stable foam. The foam was added to the unfoamed plasterslurry and blended for an additional 60 sec at 4000 rpm. To thethus-prepared slurry was added 20 wt % particles as prepared in Example1, which were mixed in by hand. The resulting mixture was poured into a6″×6″×½″ oiled glass mold faced with heavy paper stock and allowed toset for 12 hrs. The sample board was then removed from the mold anddried in a convection oven at 70° C. for 24 hrs. A measure of theacoustic attenuation was conducted using a pair of 24 kHz transducers ina pitch-catch configuration using a frequency sweep. In such a knownconfiguration, one transducer transmits a frequency against the surfaceof the sample board, while the other transducer, some distance away onthe same side of the sample board, receives the frequency as it isreflected back after propagating along the board surface. Propagationalong the board surface is highly correlated to propagation through theboard.

FIG. 4 illustrates such a configuration, with emitting transducer 400,receiving transducer 402, composite board 404, original signal 406,signal propagating through the surface of the board 408, and finally thesignal received at the second transmitter 410. A neat plaster board wasprepared in the same manner as above to serve as a control; it did notcontain any coated particles. The thus-prepared composite plaster boardexhibited 65 dB increased attenuation over the control at a centerfrequency of 3,500 Hz with 3,500 Hz bandwidth (1,750 Hz to 5,250 Hz).The bandwidth is the range over which attenuation is at least 10% of thepeak attenuation (65 dB). Thus, at least 6.5 dB of attenuation wasdemonstrated between the range from 1,750 to Hz.

Example 6: Preparation of Plaster Board with Particles from Example 2

To 1 part water was added, by sifting, 2 parts plaster, which wasallowed to soak for 1 min. The slurry was mixed in a blender for 60 secat 4000 rpm. Separately, 0.1 g of foaming agent (“MasterCell 30” fromBASF) and 4 g of water were mixed at 4000 rpm for 60 sec to generate astable foam. The foam was added to the unfoamed plaster slurry andblended for an additional 60 sec at 4000 rpm. To the thus-preparedslurry was added 20 wt % particles from Example 2, which were mixed inby hand. The resulting mixture was poured into a 6″×6″×½″ oiled glassmold faced with heavy paper stock and allowed to set for 12 hrs. Thesample board was then removed from the mold and dried in a convectionoven at 70° C. for 24 hrs. A measure of the acoustic attenuation wasconducted using a pair of 24 kHz transducers in a pitch-catchconfiguration using a frequency sweep. A neat plaster board was preparedin the same manner as above to serve as a control; it did not containany coated particles. The thus-prepared composite plaster boardexhibited 65 dB increased attenuation at a center frequency of 8,500 Hzwith 8,000 Hz bandwidth.

Example 7: Preparation of Plaster Board with Particles from Example 3

To 1 part water was added, by sifting, 2 parts plaster, which wasallowed to soak for 1 min. The slurry was mixed in a blender for 60 secat 4000 rpm. Separately, 0.1 g of foaming agent (“MasterCell 30” fromBASF) and 4 g of water were mixed at 4000 rpm for 60 sec to generate astable foam. The foam was added to the unfoamed plaster slurry andblended for an additional 60 sec at 4000 rpm. To the thus-preparedslurry was added 20 wt % particles from Example 3, which were mixed inby hand. The resulting mixture was poured into a 6″×6″×½″ oiled glassmold faced with heavy paper stock and allowed to set for 12 hrs. Thesample board was then removed from the mold and dried in a convectionoven at 70° C. for 24 hrs. A measure of the acoustic attenuation wasconducted using a pair of 24 kHz transducers in a pitch-catchconfiguration using a frequency sweep. A neat plaster board was preparedin the same manner as above to serve as a control; it did not containany coated particles. The thus-prepared composite plaster boardexhibited 60 dB increased attenuation at a center frequency of 14,000 Hzwith 15,000 Hz bandwidth.

Example 8: Preparation of Plaster Board with Particles from Examples 1,2, and 3

To 1 part water was added, by sifting, 2 parts plaster, which wasallowed to soak for 1 min. The slurry was mixed in a blender for 60 secat 4000 rpm. Separately, 0.1 g of foaming agent (“MasterCell 30” fromBASF) and 4 g of water were mixed at 4000 rpm for 60 sec to generate astable foam. The foam was added to the unfoamed plaster slurry andblended for an additional 60 sec at 4000 rpm. To the thus-preparedslurry was added 7 wt % particles from Example 1, 7 wt % particles fromExample 2, and 7 wt % particles from Example 3, which were mixed in byhand. The resulting mixture was poured into a 6″×6″×½″ oiled glass moldand allowed to set for 12 hrs. The sample board was then removed fromthe mold and dried in a convection oven at 70° C. for 24 hrs. A measureof the acoustic attenuation was conducted using a pair of 24 kHztransducers in a pitch-catch configuration using a frequency sweep. Aneat plaster board was prepared in the same manner as above to serve asa control; it did not contain any coated particles. The thus-preparedcomposite plaster board exhibited 50 dB increased attenuation at acenter frequency of 10,000 Hz with 20,000 Hz bandwidth.

Example 9: Preparation of Foam Cement Board with Particles from Example4

Unfoamed cement slurry was mixed at a water:cement ratio of 0.44 in aFann blender in accordance to API Specification 10A by mixing 141 gwater with 354 g of API Portland Class H hydraulic cement. Separately,0.1 g of foaming agent (“MasterCell 30” from BASF) and 4 g of water weremixed at 4000 rpm for 60 s to generate a stable foam. The foam was addedto the unfoamed cement slurry and blended for an additional 60 s at 4000rpm. To the thus-prepared foamed slurry was incorporated 25 wt %particles from Example 4 with a mixing blade attached to a handhelddrill until a uniform distribution of particles was achieved. Theresulting mixture was poured into a 6″×6″×½″ oiled glass mold faced withheavy paper stock and allowed to set for 12 hrs. A measure of theacoustic attenuation was conducted using a pair of 24 kHz transducers ina pitch-catch configuration using a frequency sweep. A neat plasterboard was prepared in the same manner as above to serve as a control; itdid not contain any coated particles. The thus-prepared compositeplaster board exhibited 55 dB increased attenuation at a centerfrequency of 14,000 Hz with 16,000 Hz bandwidth.

Example 10: Preparation of a Composite Sandwich Plaster Board

A composite sandwich panel was prepared by joining two plaster panelswith an elastic layer. To 1 part water was added, by sifting, 2 partsplaster, which was allowed to soak for 1 min. The slurry was mixed in ablender for 60 sec at 4000 rpm. Separately, 0.2 g of foaming agent(“MasterCell 30” from BASF) and 8 g of water were mixed at 4000 rpm for60 sec to generate a stable foam. The foam was added to the unfoamedplaster slurry and blended for an additional 60 sec at 4000 rpm. Theresulting mixture was poured into two 6″×6″×½″ oiled glass mold facedwith heavy paper stock and allowed to set for 12 hrs. The sample boardswere then removed from the mold and dried in a convection oven at 70° C.for 24 hrs. To 200 g of polydimethylsiloxane (PDMS) was added 75 g of20/40 tungsten carbide pellets. The polymer was mixed by hand until ahomogenous mixture was achieved. In the bottom of a 6″×6″×⅝″ mold wasplaced a prepared plaster board. To the top of the plaster board wasadded a ⅛″ thick layer of the polymer tungsten mixture. A preparedplaster board was placed on top of the polymer layer. The assembly waslightly clamped to allow squeeze-out of the excess polymer and to ensureeven spacing between the plaster panels. Two neat plaster boards wereprepared in the same manner as above and adhered together with epoxy toserve as a control. The thus-prepared composite plaster board exhibited50 dB increased attenuation at a center frequency of 10,000 Hz with20,000 Hz bandwidth.

Example 11: Preparation of Expanding Polyurethane Foam Board withParticles from Examples 1, 2, and 3

In another embodiment, particles from Examples 1, 2, and 3 wereincorporated into polyurethane expanding insulation foam (GREAT STUFFfrom Dow Chemical Company) to create an acoustic insulation filler. Twohundred grams of GREAT STUFF foam was discharged from the aerosolcanister into a beaker. To the foam was added 10 wt % particles fromExample 1, 10 wt % particles from Example 2, and 10 wt % particles fromExample 3, which were mixed in by hand until a uniform distribution ofparticles was observed. The foam composite was placed in a 6″×6″×1″oiled glass mold and allowed to set for 12 hrs. A control foam samplewas also produced that contained no particles. A measure of the acousticattenuation was conducted using a pair of 24 kHz transducers in apitch-catch configuration using a frequency sweep. The thus-preparedcomposite foam insulation exhibited 30 dB increased transmission loss ata center frequency of 10,000 Hz with a bandwidth of 20,000 kHz.

Example 12: Preparation of Cement Slabs with Particles from Example 1

In yet another embodiment, a large composite cement slab was preparedwith particles from Example 1. To a 5 cu. ft. rotary drum cement mixerwas added 17 kg of water and 40 kg of Portland cement (Type I-II fromHawaiian Cement). The slurry was mixed for 5 min. To the thus-preparedslurry was added 25 wt % particles from Example 1, and the slurry wasmixed for an additional 5 min. The composite slurry was poured into a20″×20″×4″ mold and allowed to set for 24 hrs. A measure of the acousticattenuation was conducted using a pair of 24 kHz transducers in apitch-catch configuration using a frequency sweep. The thus-preparedcomposite cement slab exhibited 50 dB transmission loss at a centerfrequency of 2,000 Hz with a bandwidth of 4,000 Hz compared to a cementslab with no particles.

Example 13: Testing of Enhanced Construction Materials

Impedance tube and ultrasonic acoustic testing of soundproof wallboardaccording to embodiments of the present invention were conducted todemonstrate its enhanced resistance to both airborne and structure borneacoustic transmission.

Cored (1¼″ diameter) papered gypsum wallboard samples—both an embodimentof the present invention and commercial versions, were tested accordingto a modified version of ASTM E2611-09, Standard Test Method forMeasurement of Normal Incidence Sound Transmission of AcousticalMaterials Based on the Transfer Matrix Method, using a transmission lossand impedance tube. This method measures transmission loss as a functionof frequency for airborne sound. Lightweight (light) and heavier (neat)gypsum samples (beta calcium sulfate hemihydrate, water, surfactantfoam, and no other additives) were tested along with the enhancedsamples containing the additive according to an embodiment of thepresent invention (same nominal density as light). Commercialsound-reducing construction materials A and B were also tested ascontrols. The transmission loss results are shown in FIG. 5 , while thecalculated STC (Sound Transmission Class) values and correspondingsample thickness and density measurements are shown in FIG. 6 , eachshowing results for the light 508, neat 506, enhanced 502, material A510 and material B 504 samples. In FIG. 6 , the left bar 602 isthickness in cm, the center bar 604 is the STC, and the right bar 606 isthe density in g/cc. It can be seen that the enhanced sample accordingto an embodiment of the present invention substantially outperforms theother samples in STC.

Papered wallboard samples (6″×6″×½″) were tested using an ultrasonictransducer setup with source and receiver transducers, amplifiers,signal generator, and data acquisition card. Measurements were made inan indirect mode with source and receiver on the same side of thesample. This test indicates resistance to structure-borne acoustictransmission as a function of frequency. Results for commercial boards A704 and C 702 are shown in FIG. 7 , while the results for control 802and enhanced (embodiment of the present invention) 804 boards are shownin FIG. 8 . Control and enhanced boards 802, 804 have the same densityas commercial board A 704. Again, the enhanced sample 804 substantiallyoutperforms the others.

Example 14: Preparation of Coated Stainless Steel Cores Using FluidizedBed Coater

Stainless steel (SS) shot particles were encapsulated with an elasticcoating using a fluidized bed coater. Specifically, the SS shotparticles were primed and air-dried with volatile siloxane to improvethe quality and speed of adhesion with a polymer solution. This polymersolution was prepared by dispersing polydimethylsiloxane (100% SiliconeSealant) and acrylic microspheres (thermoplastic microsphereencapsulating a gas) in mineral spirits (Odorless Mineral Spirits). Thefluidized bed coater was then charged and fluidized with the siloxaneprimed SS shot particles. During the coating process, the fluidized bedcoater was kept at a temperature of 80° C. The polymer solution (at 25°C.) was sprayed onto the primed SS shot particles with an air atomizedspray gun. The resultant coated particles were uniform in size andexhibited an equivalent degree of sphericity and roundness to thestarting core material (>0.9 Krumbein-Sloss shape factors).

The SS shot particles for this example can have a diameter ranging from0.149 to 1.680 mm. 10 to 10,000 mL of volatile siloxane can be used toprime the SS short particles before coating. For the polymer solution,between 0.85 and 170 kg polydimethylsiloxane and between 0.034 to 6.8 kgacrylic microspheres can be combined in 2.55 to 510 kg mineral spirits.The polymer solution may have 0.5-2% acrylic microspheres and a specificratio of microspheres/silicone/mineral spirits of between 1/50/150 to1/12/38. The fluidized bed coater can be charged and fluidized with5-1000 kg of the siloxane primed SS shot particles. Spraying of thesolution onto the primed SS short particles can be achieved at a rate of10-20 mL/min with the air atomized spray gun. The entire coating processmay be carried out over a period of 8-24 hrs. Resulting particles have adiameter of 0.25-4.76 mm, a coating thickness of 0.1-3.0 mm, and adensity of 2-3 g/cm³.

Example 15: Preparation and Testing of Sound Attenuating Cement andConcrete

Samples of sound attenuating cement and concrete were generated. Typicalsamples had a size of 8″×8″×2″ and a density of 16 lbs per gallon. Forthe cement samples, as a base material, Portland cement (from Quikrete)that had an appropriate water-to-cement ratio to achieve the targeteddensity (e.g., 16 lbs per gallon) was used. For the concrete samples,sand and gravel were incorporated into the cement base material, therebyresembling the concrete used in flooring. The concrete for this examplehad a ratio of 1:2:2 parts by volume of cement:gravel:sand, as well asan admixture (a liquid superplasticizer from Iksung), resulting in aratio of approximately 1:2:2:0.1 parts by volume ofcement:gravel:sand:plasticizer.

Each of two different types of sound attenuating particles were thenmixed into both the cement and concrete, generating two cement samplesand two concrete samples. Specifically, the two types of soundattenuating particles tested were: (1) stainless steel (SS) shotparticles encapsulated with a first polymer coating, and (2) tungstencarbide (WC) particles encapsulated with a second polymer coating. Therespective coating for both types of particles was applied via sprayingin a fluidized bed coater.

The first set of sound attenuation particles were generated by taking 6kg of SS shot particles (16/35 stainless steel) and applying the firstpolymer coating, which has a formulation of 1254.0 g mineral spirits,416 g silicone (737 silicone from Dow), and 11.4 g microballoons(Expancel 920 DE 80 d30 microballoons). The second set of soundattenuation particles were generated by taking 5.22 kg of tungstencarbide particles (14/24 tungsten carbide) and applying the secondpolymer coating, which has a formulation of 1386.0 g mineral spirits,460 g silicone (737 silicone from Dow), and 12.6 g microballoons(Expancel 920 DE 80 d30 microballoons). Both sets of polymer solutionswere generated by adding the mineral spirits to the silicone andstirring at 400-500 rpm for 30 min. The microballoons were then added tothe solution and further stirred at 450 rpm for 20 min. The resultantpolymer solution was filtered through a paint mesh filter, which removesunmixed chunks of the polymer solution, thereby resulting in the polymersolution being sufficiently homogenous to prevent clocking of the spraynozzle and to provide sufficient coating.

Each of the two sets of sound attenuation particles were added into thecement and the concrete at approximately 8.6 wt % of the total drymixture, resulting in homogeneous slurries with good handling properties(e.g., easy to pour and well distributed) and final cured materials withevenly distributed particles (e.g., the particles are evenly distributedand/or separated throughout the slurry and the final cement and/orconcrete block, with minimal to no agglomeration of particles).

For testing, a testing box was constructed to acoustically isolate asound meter for the impact sound transmission testing of concrete andcement samples. The box was insulated with acoustic foam and a space wasmade on the side for sound meter insertion and a hole was created at thetop for placing samples. A ball drop fixture was built for droppingsteel and rubber coated steel balls from a consistent height and placedabove the sample and box. Direct and indirect impact noises were used,either by directly dropping the ball on the surface/impacting thesurface with a rubber hammer, or by utilizing a wooden “bridge” whichallowed the impact sound to be generated just above the surface. ALarson-Davis sound meter was used to collect impact sound transmissiondata. A rubber hammer was also used to create direct and indirect impactsounds. In addition to the ball drop and hammer-based impacts, a tappingmachine (Cesva MI005) with electronically controlled impacts was used toensure that repeatable impact noises were being generated. The tappingmachine was situated above tested samples with a space below for thesound meter. The middle three hammers of the tapping machine were usedto generate impact sounds. Acoustic noise samples were recorded for tenseconds and processed for spectral analysis.

Results from direct impact hammer testing of the cement samples at highamplitude indicate a decrease in sound transmission at low frequencies.The two different sound attenuation particle types tested had differentlevels of sound attenuation in the cement samples, as shown in FIG. 9 .Trace 902 shows the behavior of a control sample, while trace 904 showsthe first set of sound attenuation materials (i.e., the SS-basedparticles) and trace 906 shows the second set of attenuation materials(i.e., the WC-based particles). As can be seen, both of the particletypes showed lowered acoustic transmission most consistently atfrequencies ranging from 8-300 Hz. At these frequencies, the cementsamples with the WC-based particles (trace 906) performed the best atreducing sound impacts.

Testing of the concrete samples from direct impact testing using theball drop and hammer as impact sources displayed a similar behavior tothe cement samples. FIG. 10 shows the behavior of a control sample(trace 1002) as compared to the concrete sample with the WC-basedparticles (trace 1004). As can be seen, the WC-based particles showreduced sound transmission over a large frequency range (e.g., a 5-12 dBdecrease at frequencies up to 300 Hz).

Finally, testing was performed on the concrete samples using the tappingmachine to create a highly repeatable impact sound. Results from thistest are shown in FIG. 11 , with a control sample (trace 1102) comparedagainst the concrete sample with the WC-based particles (trace 1104).The WC-based particles showed up to a 10 dB reduction at frequenciesranging from 10 Hz to 160 Hz.

The results of the aforementioned testing show the acoustic band gapproperties of the sound attenuation materials at low frequencies (e.g.,10 to 500 Hz), which decreases sound transmission substantially (e.g.,by 5 to 30 dB) at these frequencies.

As described above herein, a method of manufacturing sound attenuatingmaterials is disclosed, which is shown in FIG. 12 . The method 1200includes, at block 1202, adding an elastic or compliant coating to coreparticles and drying and/or curing the coating, at block 1204, mixingcoated core particles into a matrix material, and, at block 1206,pouring the mixture into a mold. The method 1200 can further include, atblock 1208, drying the mixture. The method 1200 can also include, atblock 1210, foaming the matrix material by air-entrainment,gas-entrainment, blowing agents, polyurethane reactions, or vacuumapplication.

As further described above herein, there may be multiple cores in eachof the sound attenuating particles, which is shown in the schematicdiagram of FIG. 13 . Sound attenuating particle 1302 contains multiplecores 1304.

The invention is not limited to the particular embodiments illustratedin the drawings and described above in detail. Those skilled in the artwill recognize that other arrangements could be devised. The inventionencompasses every possible combination of the various features of eachembodiment disclosed. One or more of the elements described herein withrespect to various embodiments can be implemented in a more separated orintegrated manner than explicitly described, or even removed or renderedas inoperable in certain cases, as is useful in accordance with aparticular application. While the invention has been described withreference to specific illustrative embodiments, modifications andvariations of the invention may be constructed without departing fromthe spirit and scope of the invention as set forth in the followingclaims.

What is claimed is:
 1. A sound attenuation material, comprising: aplurality of particles, each comprising a core and an elastic orcompliant coating around the core; and a matrix surrounding theplurality of particles; wherein the core is denser than the coating,wherein the coating is foamed, and wherein the plurality of particles ispan-coated, fluidized bed-coated, or both.
 2. The sound attenuationmaterial of claim 1, wherein the elastic or compliant coating comprisesfiller material having a density lower than that of the matrix.
 3. Thesound attenuation material of claim 2, wherein the filler materialcomprises polymer or glass micro-balloons.
 4. The sound attenuationmaterial of claim 1, wherein the particles are spherical.
 5. The soundattenuation material of claim 1, wherein the plurality of particlescomprises several different masses of particles.
 6. The soundattenuation material of claim 1, wherein the matrix is a constructionmaterial.
 7. The sound attenuation material of claim 1, wherein thematrix comprises gypsum, cement, concrete, polymer, or ceramic.
 8. Thesound attenuation material of claim 1, wherein the matrix comprisesreinforcing fillers, the reinforcing fillers selected from the groupconsisting of: polypropylene fibers, gravel, sand, carbon nanotubes,starch additives, paper fibers, glass fibers, and combinations thereof.9. The sound attenuation material of claim 1, wherein the core of one ormore of the plurality of particles is metal, mineral, or ceramic. 10.The sound attenuation material of claim 9, wherein the core of the oneor more of the plurality of particles is steel or tungsten.
 11. Thesound attenuation material of claim 1, wherein the elastic coating ofone or more of the plurality of particles is an elastomeric polymer. 12.The sound attenuation material of claim 11, wherein the elastic coatingof the one or more of the plurality of particles is polyurethane,silicone, or rubber.
 13. The sound attenuation material of claim 1,wherein the core of one or more of the plurality of particles has adiameter of 10 nm to 100 cm and density of 2.0 to 20 g/cc, and theelastic coating of the one or more of the plurality of particles has athickness of 10 nm to mm, an elastic modulus of 0.005 to 0.5 GPa, and adensity of 0.01 to 2.0 g/cc.
 14. The sound attenuation material of claim13, wherein the core of the one or more of the plurality of particleshas a diameter of 1 mm to 5 cm, and the elastic coating of the one ormore of the plurality of particles has a thickness of 0.1 mm to 10 mm,an elastic modulus of 0.01 to 0.1 GPa, and a density of 0.05 to 0.3g/cc.
 15. The sound attenuation material of claim 1, wherein theplurality of particles is homogenously distributed in the matrix. 16.The sound attenuation material of claim 1, wherein one or more of theplurality of particles comprises more than one core.
 17. A method ofmanufacturing sound attenuating materials, comprising: adding a foamedelastic or compliant coating to core particles and at least one of:drying the foamed coating, and curing the foamed coating, therebygenerating coated core particles; mixing the coated core particles intoa matrix material, thereby generating a mixture; and pouring the mixtureinto a mold; wherein the core particles are denser than the matrixmaterial.
 18. The method of claim 17, further comprising drying themixture.
 19. The method of claim 17, wherein the core particles have arange of masses.
 20. The method of claim 19, wherein each mass of coreparticle corresponds to a resonant frequency, wherein the masses of thecore particles are selected based on pre-selected frequencies to beattenuated by a final construction material, and wherein the proportionof each mass core particle is selected based on a predetermined desiredlevel of attenuation at the corresponding resonant frequency.
 21. Themethod of claim 17, further comprising foaming the matrix material byair- or gas-entrainment, blowing agents, polyurethane reactions, orvacuum application.
 22. A sound attenuation material, comprising: aplurality of particles, each comprising a core and an elastic orcompliant coating uniformly distributed around the core; and a matrixsurrounding the plurality of particles, wherein the core is denser thanboth the coating and the matrix, wherein the matrix is denser than thecoating, and wherein both the coating and the matrix are foamed.
 23. Thesound attenuation material of claim 22, wherein the matrix comprises anelastic material.
 24. The sound attenuation material of claim 22,wherein the coating is at least one of: dried by hot air, dried bymoisture, cured by hot air, and cured by moisture.
 25. The soundattenuation material of claim 1, wherein the coating is at least one of:dried by hot air, dried by moisture, cured by hot air, and cured bymoisture.